1. Field of the Invention
The present invention relates to a method of forming a fine pattern in a semiconductor device, and a method of manufacturing a semiconductor device having a fine pattern.
2. Background Art
A reduction-projection exposing technique has been widely used for fabricating a circuit pattern, such as an LSI. An improvement in resolution ascribable to a reduction in the wavelength of exposing radiation has recently been fostered in the field of exposure techniques. Resolution on the order of 0.1 μm is considered to become feasible as a result of employment of an ArF excimer laser (having a wavelength of 193 nm) in place of a KrF excimer laser (having a wavelength of 248 nm) which has been widely used. Further, use of the X-ray lithography technique or electron beam lithography technique is under study in an attempt to form a finer pattern.
Exposure using short wavelength light, X-ray, or an electron beam encounters a problem of deterioration in pattern geometry and resist sensitivity, which is caused by an absorption of light by a resist. In order to solve the problem, a chemically-amplified resist which absorbs less light and has a high sensitivity has been developed, and practical use of the chemically-amplified resist has been the subject of various studies. The studies have revealed problems hindering commercial mass-production of a chemically-amplified resist.
A typical problems pertaining to a chemically-amplified resist is an anomaly in the cross section of each of patterns formed on various underlying films. Particularly, in a case where an underlying film is a film containing nitrogen atoms, such as silicon nitride or titanium nitride, a tapered portion appearing at the foot of a chemically-amplified resist pattern poses a serious problem. A silicon nitride film has been widely used as an etching mask or an inorganic anti-reflection film. Patterning is indispensable for nitride-film-based material, and an anomaly of pattern geometry, such as a tapering pattern, must be avoided.
Such an anomaly of pattern geometry has been thought to be attributable to the phenomenon of acid being trapped by ammonium residing on the surface of a nitride film or by ammonium contaminated in the environment or being trapped by the lone pair of electrons of each nitrogen atom contained in a nitride film. A method of oxidizing the surface of a silicon nitride film through use of oxygen plasma has been proposed as described, for example, in Japanese Patent Application Laid-Open Nos. 83786/1996 and 134867/1997, and a method of depositing a silicon oxide film on a silicon nitride film has been proposed as described in Japanese Patent Application Laid-Open No. 10-189441. However, the experiments conducted by the inventor of the present invention has shown that the geometry of a resist pattern may be deteriorated even when the substrate laid immediately below a resist is subjected to the foregoing processing.
In an effort to solve such an anomaly of the geometry of a resist pattern, the present inventor has examined the cause of the anomaly. As a result, the inventor has found that in a case where a high-resolution chemically-amplified resist is adopted, the geometry of a resist pattern is deteriorated even when nitrogen atoms are present in a trace amount on the surface of a silicon oxide film. The deterioration is considered to stem from acid being trapped by the lone pair of electrons of each nitrogen atom which is present on the surface of a substrate.
It is considered that, in order to prevent nitrogen components from being contained in an oxide film, nitrogen-containing components must be eliminated from a source gas during the course of a CVD operation. For example, use of the plasma CVD technique and use of silane and oxygen as source gases are desirable. In a case where silane and oxygen are used, reaction readily proceeds at ordinary temperatures even if no plasma exists, thereby producing a fine powder of SiO2 in a chamber or a process gas inlet pipe. The resultant powder leads to the presence of particles on a wafer and is not desirable.
Consequently, it is desirable that a silicon oxide film be formed in only a plasma generation area without involvement of generation of particles while using, as an oxidizing gas, N2O or NO which would induce reaction only with the assistance of energy, such as that provided by plasma.